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06. Private or Protected?

One important note to make is the implementation of private in ActionScript 2.0. In languages such as Java, a private member means that only the class itself has access to it, and no access from a subclass (whether it is from the same package or not). In AS2, the implementation of private behaves more like protected in other languages; the scope is extended to subclass(es).

Because these new modifiers are checked at compile-time only, it is important to ensure that the compiler catches access to private methods and properties; this is only possible if strict-typing is used in the instance. For example, if we declare a property as private:

class PrivateMemberClass {
   private var privateProp:String = "I'm a private property";
}

var instance = new PrivateMemberClass();
trace(instance.privateProp); // output "I'm a private property"

var instance:PrivateMemberClass = new PrivateMemberClass();
trace(instance.privateProp); // compile error

This is one of the most common mistakes that people make and then wonder why private members are accessible. So now you know!

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